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Hajrah Tabassam Supervisor: Victoria Martin University of Edinburgh

Prospects for the top Yukawa coupling from e + e − ➞ t̅ tH ➞ b̅W − bW + b̅ b (Status of the Analysis). Hajrah Tabassam Supervisor: Victoria Martin University of Edinburgh. Contents. Introduction Sample Lepton Identification Missing Energy reconstruction

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Hajrah Tabassam Supervisor: Victoria Martin University of Edinburgh

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  1. Prospects for the top Yukawa coupling from e+ e−➞ t̅ tH ➞ b̅W− bW+ b̅ b(Status of the Analysis) Hajrah Tabassam Supervisor: Victoria Martin University of Edinburgh

  2. Contents • Introduction • Sample • Lepton Identification • Missing Energy reconstruction • Semi-Leptonic W reconstruction • Jets Reconstruction • Full event reconstruction • Background and Signal Separation • Conclusion • Future Plans

  3. Introduction • Once Higgs is found, its coupling with fermions is interesting to study. • is vacuum expectation value of Higgs field. • Top is heaviest fermion, so top-Higgs Yukawa coupling is largest. • The coupling of top to the Higgs is modified in the SUSY models • This analysis was not done for LOI • ILD software framework is used for this analysis

  4. Samples • ILD_00 centrally reconstructed sample with center of mass energy √s = 500 GeV. • t t̅-Higgs events with Mh = 120 GeV/c2, Mt = 175 GeV/c2. * Number of events used in the analysis so far corresponds to luminosity L = 34 ab−1 ** Currently our only background is t t̅Z which often mimic the signal We will include other backgrounds at a later stage but due to their different topology, it will be easy to get rid most of them.

  5. Semi-Leptonic Channel • e+ e−➞ t̅ tH ➞ b̅W− bW+ b̅ b • Focus on semi-leptonic final state with one W decaying into lepton and neutrino and other W decaying into light jets • Final state is 1 lepton, missing energy, 6 Jets with 4 b-jets • Remove the leptons and force remaining particles into 6-jets (JetFinder Algorithm) • High momentum Lepton and large missing momentum signature

  6. Filtering of Semi-Leptonic Channel for Monte Carlo Sample • Initially 20,000 MC events with full final state where Higgs and W decay into anything • Filter events with one lepton (μ, e), and H decaying to bb̅, 4466 events are left.

  7. Lepton Identification(From study of Single MC Lepton with P >15 GeV) • Muon Identification: • Cut based selection is being used. Efficiency from single Muon sample is 98%. (1) EEcal < 2.5 GeV (2) EHcal < 15 GeV (3) EEcal / ETot < 0.5 (4) Etot / p < 0.3 • Electron Identification: • Cut-based selection on single Electron sample has showed that 98.57% electron are identified by using: (1) EEcal / ETot > 0.6 (2) ETot / p > 0.7

  8. W ➞νl (Lepton Identification) • we identify our reconstructed leptons (e, μ) using same cut variables as for single lepton case. • Most of the reconstructed leptons are correctly identified as leptons. • These lepton tracks are then removed from the PandorPFOs collection.

  9. W ➞νl (Missing Momentum) • Using the information for all reconstructed particles, missing momentum is reconstructed. • Z-component of missing energy isn’t as accurate as x and y components • However, z-component can be used to reconstruct Semi-leptonic W mass.

  10. W ➞νl (Transverse Mass) • To reconstruct semi-leptonic W, we select events which have lepton momentum not equal to zero and one lepton with highest momentum • The transverse momentum of lepton and Missing Momentum are used to reconstruct the transverse mass of W. True Transverse Mass of W (GeV) True M_LepT (GeV)

  11. Jets reconstruction • Identified leptons are removed from the sample • remaining particles are forced into 6 Jets using JetFinder algorithm • Jets pass LCFIVertex reconstruction [arXiv:0908.3019v1] • LCFI flavour tagging is used to separate light and b-jets • Jets are sorted in descending order of b-tag value • top four jets with highest b-tag value are selected as b-jets • Light jets are used to reconstruct hadronic W

  12. Final State Reconstruction • As we have a good reconstruction of z-component of the missing momentum, it is used to reconstruct the Mass of semi-leptonic W • Four b-jets are used to reconstruct two tops and Higgs particle • To reduce combinatorial backgrounds, minimisation of χ2technique is used currently we have set σ’s equals to one GeV.

  13. Reconstructed Final State There are 12 entries for each event due to different combinations

  14. Reconstructed Final State after Minimizing χ2

  15. Selection variables selected ttH ttZ selected Signal and background are arbitrarily normalised Cuts are selected by optimising S/√(S+B)

  16. b-tagging • B-tag of all 6 jets are looked at • 4 with largest b-tag value are considered as b-jets • Cut on b-tag values of jet3 and jet4 can reduce a significant number of background events

  17. b-tag efficiency (3rd and 4th Jets)

  18. Signal and Background separation

  19. Signal and Background Final State after applying selection cuts Signal and background are arbitrarily normalised

  20. Summary/Future Plans • Reconstruction of final state for analysis of Top-Higgs Yukawa coupling is presented and results will be soon ready • Higgs reconstruction would benefit from taken out of the χ2 formula • Using other variables to reduce more background contamination and hence optimise selection • Multivariate will be used to improve the background suppression • It will be necessary to extended this study to a higher energy but b-tagging will needed to be optimised • We are intended to do this study for CLIC

  21. Extra slides

  22. Cross section of t̅ tH

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